The present invention discloses a vehicle electrical system comprising a generator delivering electrical power to an electrical load. The generator includes two field coils, each generating a magnetic flux and each interacting with one or more stator windings operative to generate the electrical power. Each field coil is coupled with a switch circuit which is operated upon by a control device. The control device monitors and controls the switch circuits to regulate the generator output voltage. Both simultaneous and sequential switching of the two field coils, via the two switch circuits, maybe implemented. The control device may be concurrently configured to ascertain the operating states of the switch circuits and controllably reconfigure and/or deactivate the switch circuits based on the operating states. The operating states may be further communicated to the vehicle electrical system. An electrical energy absorbing device may be coupled with the generator via a switch and the control device may be further configured to apply one or more control signals to the switch facilitating voltage transient suppression and generator drive system protection due to generator deceleration and/or vehicle operating condition.
The generator includes two independent field coils in order to lower the electrical field current in each of the two field coils while providing the same electrical output power that could be obtained through a single but larger field coil. Using two smaller independent field coils instead of one large field coil in the generator is advantageous because it allows the generator to operate, at least at half power, when a malfunction occurs. The malfunction could be due to the field coil or switching circuit. A single malfunctioning field circuit, comprising of the field coil and the switch circuit, renders the generator inoperable whereas a generator with two field circuits, each comprising of a field coil and a switch circuit, can operate at half power even when one of the field circuits fails.
A further advantage is realized during sudden disconnection of the electrical load. Known to artisans of ordinary skill, sudden removal of the electrical load causes the generator to exhibit large voltage transients due to slow dissipation of the large electrical energy stored in a single field coil. Utilizing two field coils reduces the electrical current in each of the two field coils, reduces the magnitude of the stored electrical energy in each of the two field coils, dissipates the stored electrical energy faster and, therefore, substantially decreases the voltage transients due to sudden removal of the electrical load.
Each switch circuit can have multiple switches for redundancy and improved protection. See, for instance, Jabaji, U.S. Pat. No. 7,276,804 and its progenies, incorporated herein by reference in their entireties. In a preferred embodiment, two switches are used in each of the two switch circuits and the control device is configured to controllably reconfigure and/or deactivate one or both switch circuits. Accordingly, the generator can continue to produce electrical power even when a switch malfunctions. In the event the switch circuits cannot be reconfigured, the control device may be configured to deactivate the switch circuit associated with the malfunctioning field circuit.
An electrical energy absorbing device such as a resistor, a metal oxide varistor, or a zener diode may be coupled with the generator to reduce voltage transients and to protect the generator drive system. The electrical energy absorbing device may be used to dump electrical power in it when the electrical load is suddenly removed. This will further reduce the associated voltage transient. The electrical energy absorbing device may be used further to provide a braking load on the generator rotor during generator deceleration or vehicle shutdown, thereby, protecting the generator drive system.
Vehicle electrical systems are normally comprised of an electrical load and a generator, including a voltage regulator, supplying electrical power to the electrical load. Such electrical load includes, but is not limited to, one or more stored energy sources, instrumentation, electronic vehicle control systems, heating elements, lights, stereo systems, wiring system, and/or any other electrical device which may either supply or consume electrical energy to or from said vehicle electrical system. The generator supplies electrical power to the vehicle electrical system when the vehicle's engine is operating. The voltage regulator's primary function is to regulate the generator's output power at a specific reference voltage. Modern voltage regulators also function to monitor and control the generator's performance to protect the vehicle electrical system. (See, Becker et al., U.S. Pat. No. 6,184,661, and Jabaji, U.S. Pat. No. 5,907,233.)
Conventional voltage regulators operate to maintain the output voltage of the generator at a constant voltage. As the number and operational complexities of electronic components in the vehicle electrical system increase, the voltage regulator must accordingly provide system monitoring and protection in addition to voltage regulation. As such, control devices are utilized that couple with generators to monitor and manage electrical power distribution throughout the electrical system in addition to maintaining the output voltage of the generator at a regulation/common/system voltage.
For instance, the commonly assigned U.S. Pat. No. 7,276,804, entitled “Voltage Regulator with Improved Protection and Warning System” and its progenies hereby incorporated by reference in their entireties, discloses a vehicle electrical system voltage regulator with improved electrical protection and warning means that discerns and responds to regulator, generator, or vehicle electrical system operation and malfunctions. The regulator includes monitoring, control, and protection circuits with a phase signal monitor, a field switching circuit that operates the field coil in response to electrical power demands, and a field enable switch in series with the field regulating switch. The phase monitor and protection circuit ascertains and transmits generator rotational motion for use by the monitoring and control circuit in discerning the various operating conditions. The monitoring and control circuit operates on the field switching circuit to meet the electrical power demands and provide multi level fault protection to include field switching circuit reconfiguration to continue operating under various fault conditions. A warning and diagnostic system incorporating visual indicators and communication lines provide descriptive system information for use by the vehicle's operator and computer network, respectively.
In the commonly assigned U.S. Pat. No. 6,184,661, entitled “Regulator with Alternator Output Current and Input Drive Power Control,” hereby incorporated by reference in its entirety, an alternator regulator controls both output voltage and output current, limits input drive power and torque, and maintains output power within a prescribed range while operating over a wide ambient temperature range and shaft speed range. Voltage, shaft speed, and temperature signals are monitored, and the results are processed to determine the output current and to control the output power without exceeding the programmed limits for output voltage, output current, temperature, output power, drive power, torque, and shaft speed. This provides a predictable output power characteristic for the alternator and it eliminates high input drive power and torque excursions that occur at low temperature and certain shaft speeds. If programmed limits are exceeded over a specified interval, and the alternator does not respond to the control changes imposed by the regulator, the regulator will turn off the alternator's field current, activate an alarm circuit, and set fault codes. The regulator is also capable of communicating with other control systems to provide status, specify needs, and respond to requests.
Incorporating and applying these technologies to a high electrical output power generator with two independent field coils substantially improves its performance. Electrical systems, such as those implemented in modern vehicles, include complex electronics and electrical equipment. Such electrical systems are normally comprised of an internal combustion engine and a generator. The engine supplies the generator with mechanical power, via a drive system, and the generator converts it into electrical power for the electrical system consumption. As the number of electrical components increase, the generator's electrical output power must also increase. This is accomplished by increasing the size of the generator, specifically, by increasing the magnitude of its magnetic flux. As a result, larger field coils are utilized to produce the required magnetic flux.
In a vehicle electrical system where a generator is used to meet all the electrical power demand by various electrical components, proper protection of the generator becomes essential to maintaining the operational integrity of the vehicle electrical system. In particular, the generator's field circuit, comprising of the field coil and its switch circuit, must be well protected because they are the source of its output power. A generator with a single faulty field circuit renders the vehicle electrical system inoperative, whereas a generator with two independent field coils, one faulty and one operational, continues to function as if there is no fault assuming only one half (½) of maximum power is required. Even at maximum power condition, the generator continues to provide electrical power, albeit at a lower voltage.
The generator is controlled by a control device. See, for example, Jabaji, U.S. Pat. No. 7,276,804. For improved protection, the control device operates on two switch circuits which are coupled with the generator's two field coils. In a preferred embodiment, each switch circuit comprises two switches. Ordinarily, one switch operates to vary the field current in the field coil, while the other protects against overvoltage condition. The control device includes an analog or digital processor that operates on the switches. When two such switch circuits are utilized in the same electrical system, it is advantageous to provide the control device with the capability of reconfiguring and/or deactivating the switch circuits in the event of a temporary malfunction or a complete breakdown. Therefore, it becomes necessary to monitor, discern, communicate and respond to such events so that the vehicle electrical system may continue normal operation without the use of additional redundant components.
Ascertaining and responding to the operating conditions of the generator and switch circuits is desirable and/or required in order to ensure that the vehicle electrical system operates without interruption. Other sophisticated electrical systems have been employed to ensure that the electrical power delivery is managed as a function of the vehicle operating conditions. For instance, in the commonly assigned U.S. Pat. No. 7,202,574 entitled “System and Method for Electric Energy Switching and Control in a Vehicle,” and its progenies, hereby incorporated by reference in their entireties, a control device determines the vehicle's operating conditions and facilitates the transfer of electrical energy between systems of electrical energy sources and their associated electrical loads based on the vehicle operating conditions. The device further determines the operating conditions of the systems of electrical energy sources and their associated electrical loads and facilitates the transfer of electrical energy between them in accordance with said operating conditions.
The present invention seeks to provide a generator with two independent field coils, coupled with two switch circuits, and a control device which operates on the switch circuits to regulate the generator output voltage and supply continuous electrical power even when a fault occurs. This can be accomplished by utilizing two field circuits which are operated independently by a single control device capable of monitoring their operations and reconfiguring and/or deactivating them when necessary. In addition, the invention seeks to improve on transient response and drive system protection.
Although various systems have been proposed which touch upon some aspects of the above problems, they do not provide solutions to the existing limitations in providing a generator with two independent field circuits. For example, Mukai et al., U.S. Pat. No. 7,429,802 discloses a vehicle-use generator which includes a first rotor core having a first field coil wound therearound, a second rotor core having a second field coil wound therearound, a rotating shaft belt-driven by a vehicle engine, the first and second rotor cores being mounted in tandem on the rotating shaft, a stator core having a stator coil wound therearound, and disposed radially outwardly of the first and second rotor cores so as to form a circumferential gap with the first and second rotor cores. The first and second field coils are connected substantially in parallel to each other when viewed from an external field current supply source supplying field currents to the first and second field coils. However, in Mukai's generator the field coils are mounted on the shaft and rotating with the shaft, whereas the vehicle electrical system, control device, and methods of operation are not limited to such generators. In addition, the operating conditions of the switch circuits in the present invention are monitored and responded to by the control device, whereas Mukai provides no such monitoring or control.
Hotta et al., U.S. Pat. No. 5,177,388 discloses a tandem type alternator which comprises a rotor rotatably supported inside a housing and having rotor cores having magnetic poles formed on outer peripheral portions of the rotor cores, respectively, and a plurality of stators arranged on an inside wall of the housing and in tandem in the direction of the axis of rotation of the rotor and having tooth-shaped stator cores which are positioned to be opposite to the magnetic poles of the rotor cores and on which multi-phase windings are wound, respectively. The stators have respectively the multi-phase windings wound thereon so that both multi-phase windings are shifted from each other in the direction of the axis of rotation of the rotor. The housing has ventilation window portions formed between and near the plurality of stators which provide communication between the interior and exterior of the housing, so that ventilation resistance within the housing is reduced and the cooling effect is increased. However, Hotta's alternator has rotating field coils and its control circuit does not control the switch circuits according to the operating states.
Radomski, U.S. Pat. No. 4,882,515 discloses an alternating current generator for supplying the electrical loads on a motor vehicle. The generator has a stator core that carries a three-phase stator or output winding. The rotor of the generator has two claw pole members that are so oriented that the fingers of the pole members are aligned. Disposed between the two pole members is a third pole member having projections disposed between the aligned fingers of the claw pole members. The rotor has two field coils which are so arranged and energized that the magnetic polarity of the two claw pole members is the same and opposite the magnetic polarity of the third pole member. One of the field coils can be replaced by a permanent magnet and when this is done the generator is provided with a magnetic circuit that can divert permanent magnet flux away from the stator core. Flux diversion is controlled by supplying unidirectional current to the field winding under the control of a voltage regulator. Radomski's generator also suffers from the same limitation of being limited to rotating field coils and control circuit lacking control over the switch circuits according to their operating conditions.
Generators, delivering large electrical power, can benefit from utilizing two independent field circuits. A vehicle electrical system which includes such generator would also benefit from using a single control device which can further respond to the field circuits' operating conditions. Transient effects due to sudden disconnection of such large electrical loads can be very detrimental to other electrical components in the vehicle electrical system and suppression of such transients is necessary. Protection of the generator drive system also becomes essential when large mechanical power is applied to the generator.
The present invention offers a simple, yet efficient, alternative to existing technologies by incorporating a single controller which controls two independent field coils. In particular, the control device controls two field circuits of a high electrical output generator while responding to their operating states. In addition, the control device operates on an electrical energy absorbing device, via a switch, to further suppress transient effects and protect the drive system.